Cell signaling via 3′-phosphorylated phosphoinositides has been implicated in a variety of cellular processes, e.g., malignant transformation, growth factor signaling, inflammation, and immunity (Rameh et al., J. Biol. Chem., 274:8347-8350, 1999). Phosphatidylinositol 3-kinase (PI 3-kinase or PI3K) is responsible for generating these phosphorylated signaling products. PI3K was initially identified as a protein associated with viral oncoproteins and growth factor receptor tyrosine kinases that phosphorylate phosphatidylinositol (PI) and its phosphorylated derivatives at the 3′-hydroxyl of the inositol ring (Panayotou et al., Trends Cell Biol., 2:358-60, 1992).
Three classes of the PI 3-kinase (PI3K) are proposed based on the substrate specificities. Class I PI3Ks phosphorylate phosphatidylinositol (PI), phosphatidylinositol-4-phosphate, and phosphatidylinositol-4,5-biphosphate (PIP2) to produce phosphatidylinositol-3-phosphate (PIP), phosphatidylinositol-3,4-biphosphate, and phosphatidylinositol-3,4,5-triphosphate, respectively. Also, Class II PI3Ks phosphorylate PI and phosphatidylinositol-4-phosphate, and Class III PI3Ks phosphorylate PI.
The initial purification and molecular cloning of PI 3-kinase revealed that it was a heterodimer consisting of p85 and p110 subunits (Otsu et al., Cell, 65:91-104, 1991; Hiles et al., Cell, 70:419-29, 1992). Later, four distinct Class I PI3Ks were identified and designated as PI3K α, β, δ, and γ isoforms. Each isoform consists of a distinct 110 kDa catalytic subunit and a regulatory subunit. The catalytic subunits of PI3K α, β, and δ (i.e., p110α, p110β, and p110δ, respectively) interacts, individually, with the same regulatory subunit p85, whereas the catalytic subunit of PI3K γ (p110γ) interacts with a distinct regulatory subunit p101.
Studies have also showed that each PI3K isoform has distinct expression pattern. For example, PIK3CA which encodes PI3Kα is frequently mutated in human cancers (Engelman, Nat. Rev. Cancer, 9: 550-562, 2009). Also, PI3Kδ is generally expressed in hematopoietic cells. Moreover, PI3K isoforms are shown to be associated with proliferation or survival signaling in cancers, inflammatory, or autoimmune diseases. As each PI3K isoform has different biological function, PI3K isoforms are potential targets to treat cancer or other disorders (U.S. Pat. Nos. 6,800,620; 8,435,988; 8,673,906; US Patent Application Publication No. US2013/0274253).
Therefore, there is a need for developing therapeutic agents that inhibit PI3K isoforms to treat diseases, disorders, or conditions that are mediated by PI3K.